Choice of Intracoronary Imaging: When to use Intravascular Ultrasound or Optical Coherence Tomography Sudheer Koganti, 1,2 Tushar Kotecha 2,3 and Roby D Rakhit 2,3 1. Barts, Heart Centre; 2. University College London Institute of Cardiovascular Science; 3. Royal Free Hospital, London, UK
Abstract Intracoronary imaging has the capability of accurately measuring vessel and stenosis dimensions, assessing vessel integrity, characterising lesion morphology and guiding optimal percutaneous coronary intervention (PCI). Coronary angiography used to detect and assess coronary stenosis severity has limitations. The 2D nature of fluoroscopic imaging provides lumen profile only and the assessment of coronary stenosis by visual estimation is subjective and prone to error. Performing PCI based on coronary angiography alone is inadequate for determining key metrics of the vessel such as dimension, extent of disease, and plaque distribution and composition. The advent of intracoronary imaging has offset the limitations of angiography and has shifted the paradigm to allow a detailed, objective appreciation of disease extent and morphology, vessel diameter, stent size and deployment and healing after PCI. It has become an essential tool in complex PCI, including rotational atherectomy, in follow-up of novel drug-eluting stent platforms and understanding the pathophysiology of stent failure after PCI (e.g. following stent thrombosis or in-stent restenosis). In this review we look at the two currently available and commonly used intracoronary imaging tools – intravascular ultrasound and optical coherence tomography – and the merits of each.
Keywords Intracoronary imaging, intravascular ultrasound, optical coherence tomography Disclosure: The authors have no conflicts of interest to declare. Received: 13 January 2016 Accepted: 8 February 2016 Citation: Interventional Cardiology Review, 2016;11(1):11–6 DOI: 10.15420/icr.2016:6:1 Correspondence: Roby Rakhit, Consultant Interventional Cardiologist, Department of Cardiology, Royal Free Hospital, Pond Street, London, NW3 2QG, UK. E: email@example.com
Intracoronary imaging is able to aid the interventional cardiologist in the characterisation of atherosclerotic plaque morphology, in optimising stent sizing, and in minimising the complications associated with percutaneous coronary intervention (PCI). Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) are commonly used methods, while newer spectroscopic methods are under development.
is possible with radiofrequency-based technology such as IVUS virtual histology.2 IVUS virtual histology may assist in characterisation of plaque morphology by differentiating between various types of plaque using colour coding. As a result of limited resolution, IVUS cannot reliably identify the separation between intima and media and the relation between adventitia and peri-adventitial structures (see Figure 1).3
Intravascular Ultrasound Versus Optical Coherence Tomography: Technology
In contrast to IVUS, intracoronary imaging by OCT is obtained using near-infrared light. The first generation of OCT imaging was based on occlusive balloon technology called time domain (TD) imaging. Use of frequency domain (FD) imaging, also referred to as Fourier domain spectral imaging, has now surpassed TD imaging.4 FD imaging does not require occlusion of the proximal artery with a balloon as high viscosity liquids such as contrast media can be used to purge blood from the vessel, while imaging is completed rapidly. Current commercially available OCT catheters consist of a single-mode optical fibre in a hollow metal wire torque that rotates at a speed of 100 rps. The axial and lateral resolutions of OCT are 10–20 μm and 20 μm, respectively – which is superior to that of IVUS. However, better resolution comes at a drawback of limited penetration – a maximum of 2 mm.5 With acquisition speeds of up to 25 mm/s, rapid imaging of coronary artery can be achieved within a few seconds. Commercially available OCT catheters can be inserted into coronary artery on a 0.014 inch guide wire and are compatible with guiding catheters sized 5Fr or larger. For optimal imaging quality, a bloodless field is required, which can be achieved with injection of 12–15 ml of
Table 1 displays a technical comparison of the IVUS and OCT imaging methods. The principle of IVUS imaging is based on the ultrasound waves produced by the oscillatory movement of a transducer.1 Commercially available IVUS systems have transducers mounted on catheters that are compatible with guiding catheters in sizes of 5Fr or larger. These catheters can be inserted into the coronary artery over a 0.014 inch conventional guide wire and imaging can be obtained by manual or motorised pullback. Motorised pullbacks are carried out at a speed of 0.5 mm/s, thus a 50 mm coronary artery can be imaged in approximately 90s. Integrated IVUS consoles add to the rapidity of imaging, but mobile IVUS carts are also available. When co-registration of IVUS with angiography becomes available, this will be a useful adjunct in locating the anatomical lesion precisely. Once the pullback is recorded, measurements of the lumen can be carried out either manually or using automated software. Greyscale IVUS has an axial resolution of 100–150 μm, lateral resolution of 200 μm1 and penetration depth of 4–8 mm. Post-processing of greyscale IVUS images
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ICR 11.1 Interventional Cardiology Review Volume 11 Issue 1 Spring 2016